@jamesobutler hi,
I just compiled SLicer 4.11.20200930 git tag with MSVC 2019 and Qt 5.14.2
I still got the error:

But I can skip it and continue to normally launch Slicer.
The main question is still undclear, how to open Slicer project and debug Slicer in Qt?
I follow this documentation Documentation/Nightly/Developers/Tutorials/QtCreator - Slicer Wiki
I typed:

and with MSVC 2019 Qt 5.15.2 it doesn’t give platform plugin error anymore. That is good. After I press ENTER nothing happens. THose two lines in CMD are shown.
and this is how my project is look like:
